1. Field of the Invention
The present invention generally relates to a suspension or solution having transition metal oxide, and more particularly to a suspension or solution having transition metal oxide for an organic optoelectronic device, methods of making same, and applications thereof.
2. Description of the Prior Art
Organic optoelectronic devices, such as organic solar cells (OSC), organic light emitting diodes (OLED), organic light sensors, and so on, have many advantages. For example, the organic optoelectronic devices can be light-weight, thin, large-area, flexible, and low-cost devices.
In order to increase the power conversion efficiency of the organic optoelectronic device, a buffer layer can be disposed between an organic layer and electrode of the device. For example, a thin layer composed of calcium or lithium fluoride can be disposed between the aluminum electrode and the organic layer. A buffer layer including poly(3,4-ethylenedioxythiophene), or PEDOT, can be disposed between the transparent electrode and the organic layer so as to increase the power conversion efficiency.
However, the aluminum of such an electrode, the calcium, or the lithium fluoride can be easily oxidized in the presence of air, which may cause an increased resistance of the device. Moreover, due to PEDOT being corrosive, the transparent electrode can be easily damaged by the presence of PEDOT.
In order to address the problems described above, efforts have been made to replace the aluminum electrode with a high work-function metal to be used as a cathode, and with transition metal oxides, such as vanadium oxide or tungsten oxide, being formed between the cathode and the organic layer for transporting or injecting holes effectively so as to increase the power conversion efficiency. Moreover, another transition metal oxide, zinc oxide, which is not corrosive, can be formed between the transparent electrode (anode) and the organic layer. The zinc oxide can be used as an electron transporting or electron injecting layer in place of PEDOT.
The transition metal oxide layers described above are usually formed using a vacuum evaporation process. The cost of making such layers, however, is high, and it is difficult to produce a large-area device. Some transition metal oxide layers can be formed by the sol-gel method. While it is possible to produce a large-area device using the sol-gel method, the sol-gel method includes a high temperature annealing treatment. Consequently, the processing temperature is usually higher than the glass transition temperature (Tg) of the organic material, which may result in damage to the organic layer.